This invention relates to a multi-stage hydrocarbon treatment process with interstate injection of a quenching fluid and more particularly to vapor phase alkylation of an aromatic substrate with an alkylating agent with interstage injection of a quenching fluid comprising at least one of the aromatic alkylating agent and the aromatic substrate.
Hydrocarbon treatment processes in which a hydrocarbon reaction component is reacted with a second reaction component which may be a hydrocarbon or a non-hydrocarbon are well known in the chemical processing industry. An important aspect of such processes are aromatic conversion processes which are carried out over molecular sieve catalysts. Such aromatic conversion reactions include the alkylation of aromatic substrates such as benzene to produce alkyl aromatics such as ethylbenzene, ethyltoluene, cumene or higher aromatics and the transalkylation of polyalkyl benzenes to monoalkyl benzenes. Typically, an alkylation reactor which produces a mixture of mono- and poly- alkyl benzenes may be coupled through various separation stages to a downstream transalkylation reactor. Such alkylation and transalkylation conversion processes can be carried out in the liquid phase, in the vapor phase or under conditions in which both liquid and vapor phases are present.
Alkylation and transalkylation reactions may occur simultaneously within a single reactor. For example, where various series-connected catalyst beds are employed in an alkylation reactor as described below, it is a conventional practice to employ interstage injection of the aromatic substrate between the catalyst beds in order to control the temperature of the adiabatic process, which tends to enhance transalkylation reactions within the alkylation reactor. Without having cooling, the by-product (xylene) yield is too high. For example, in the ethylation of benzene with ethylene to produce ethylbenzene, the alkylation product within the reactor includes not only ethylbenzene but also polyethylbenzene, principally diethylbenzene with reduced amounts of triethylbenzene, as well as other alkylated aromatics such as cumene and butylbenzene. The interstage injection of the ethylene results not only further in alkylation reactions but also transalkylation reactions where, for example, benzene and diethylbenzene undergo transalkylation to produce ethylbenzene. Thus, even though a separate transalkylation reactor is connected downstream through a series of separation stages, it is the accepted practice to minimize polyalkylation within the alkylation reactor in order to facilitate the subsequent treatment and separation steps.
An example of vapor phase alkylation is found in U.S. Pat. No. 4,107,224 to Dwyer. Here, vapor phase ethylation of benzene over a zeolite catalyst is accomplished in a down flow reactor having four series-connected catalyst beds. The output from the reactor is passed to a separation system in which ethylbenzene product is recovered, with the recycle of polyethylbenzenes to the alkylation reactor where they undergo transalkylation reactions with benzene. The Dwyer catalysts are characterized in terms of those having a constraint index within the approximate range of 1-12 and include, with the constraint index in parenthesis, ZSM-5 (8.3), ZSM-11 (8.7), ZSM-12 (2), ZSM-35 (4.5), ZSM-38 (2), and similar materials.
U.S. Pat. No. 4,520,220 to Watson et al discloses the use of silicalite catalysts having an average crystal size of less than 8 microns and a silica/alumina ratio of at least about 200 in the ethylation of an aromatic substrate such as benzene or toluene to produce ethylbenzene or ethyltoluene, respectively. As disclosed in Watson et al, the alkylation procedure can be carried out in a multi-bed alkylation reactor at temperatures ranging from about 350xc2x0-500xc2x0 C. and, more desirably, about 400xc2x0-475xc2x0 C., with or without a steam co-feed. The reactor conditions in Watson et al are such as provide generally for vapor phase alkylation conditions.
Another procedure employing silicalite and involving the ethylation of benzene under vapor phase reaction conditions coupled with the recycle of polyethylbenzene containing products back to the alkylation reactor is disclosed in U.S. Pat. No. 4,922,053 to Wagnespack. Here, alkylation is carried out at temperatures generally in the range of 370xc2x0 C. to about 470xc2x0 C. and pressures ranging from atmospheric up to about 25 atmospheres over a catalyst such as silicalite or ZSM-5. The catalysts are described as being moisture sensitive and care is taken to prevent the presence of moisture in the reaction zone. The alkylation/transalkylation reactor comprises four series-connected catalyst beds. Benzene and ethylene are introduced into the top of the reactor to the first catalyst bed coupled by recycle of a polyethylbenzene fraction to the top of the first catalyst bed as well as the interstage injection of polyethylbenzene and benzene at different points in the reactor.
Another process involving the use of a silicalite as an alkylation catalyst involves the alkylation of an alkylbenzene substrate in order to produce dialkylbenzene of a suppressed ortho isomer content. Thus, as disclosed in U.S. Pat. No. 4,489,214 to Butler et al, silicalite is employed as a catalyst in the alkylation of a monoalkylated substrate, toluene or ethylbenzene, in order to produce the corresponding dialkylbenzene, such as ethyltoluene or diethylbenzene. Specifically disclosed in Butler et al is the ethylation of toluene to produce ethyltoluene under vapor phase conditions at temperatures ranging from 350xc2x0-500xc2x0 C. As disclosed in Butler, the presence of ortho ethyltoluene in the reaction product is substantially less than the thermodynamic equilibrium amount at the vapor phase reaction conditions employed.
U.S. Pat. No. 5,847,255 to Ghosh et al discloses vapor phase alkylation with separate transalkylation in which the output from the transalkylation reactor is recycled to an intermediate separation zone. The Ghosh et al process employs a multi-stage alkylation reactor in which four or more series-connected catalyst beds are employed in a downflow vapor phase reactor. Both benzene and ethylene are applied to the inlet of the reactor along with interstage injection of ethylene and/or benzene between the catalyst stages. Here, a benzene separation zone, from which an ethylbenzene/polyethylbenzene fraction is recovered from the bottom with recycling of the overhead benzene fraction to the alkylation reactor, is preceded by a prefractionation zone. The prefractionation zone produces an overhead benzene fraction which is recycled along with the overheads from the benzene column and a bottom fraction which comprises benzene, ethylbenzene and polyethylbenzene. Two subsequent separation zones are interposed between the benzene separation zone and the transalkylation reactor to provide for recovery of ethylbenzene as the process product and a heavier residue fraction. The polyethylbenzene fraction from the last separation zone is applied to the transalkylation reactor and the output there is applied directly to the second benzene separation column or indirectly through a separator and then to the second benzene separation column. In Ghosh et al, the ratio of benzene (or other aromatics substrate) and alkylating agent can be varied along the length of the reactor with the introduction of one or both reactants into the reactor at locations between catalyst beds. Any suitable technique can be employed to accomplish the interstage introduction of reactants into the reactor, but a typical system comprises a sparger, comprising a header which supplies feed stock into a plurality of sparger tubes within the header.
In accordance with the present invention, there is provided a multi-stage hydrocarbon treatment process in a multi-stage reaction zone having a plurality of series-connected catalyst beds each containing a hydrocarbon reaction catalyst and spaced from one another to provide an intermediate mixing zone between adjacent catalyst beds. A processing feedstock containing a hydrocarbon substrate component and a normally gaseous-reacting component for reaction with said substrate component to produce a reaction product is supplied to the inlet side of the reaction zone. The reaction zone is operated under temperature and pressure conditions in which the hydrocarbon substrate component is in the gas phase to cause a gas phase reaction of the components to produce the desired reaction product in the presence of the catalyst. A quench fluid comprising at least one of the hydrocarbon substrate component and the reactant component is injected into at least one intermediate mixing zone between adjacent catalyst beds. This quench fluid is dispensed into the interior of the mixing zone through a plurality of flow paths in which one portion of the flow paths is directed upwardly within the mixing zone and another portion directed downwardly within the mixing zone. The reaction product produced by the reaction of the hydrocarbon substrate component and the reactant component is recovered from a down-stream outlet of the reaction zone.
In accordance with a preferred embodiment of the present invention, there is provided a process for the vapor phase alkylation of an aromatic substrate in a multi-stage alkylation reactor employing intermediate mixing zones. In carrying out the invention, there is provided a multi-stage reaction zone having a plurality of series-connected catalyst beds containing a molecular sieve aromatic alkylation catalyst. The catalyst beds are spaced from one another to provide mixing zones between adjacent catalyst beds. A feedstock containing an aromatic substrate and a C2-C4 alkylating agent is supplied to an inlet side of the reaction zone. The reaction zone is operated at temperature and pressure conditions in which the aromatic substrate is in the gas phase and causing vapor phase alkylation of the aromatic substrate as the aromatic substrate and the alkylating agent flow through the reaction zone and pass from one catalyst bed to the next. In at least one intermediate mixing zone between adjacent catalyst beds a quench fluid comprising one or both of the aromatic substrate and the alkylating agent is supplied into the interior of the mixing zone through a plurality of flow paths. In the flow paths, one portion of the flow paths is directed upwardly within the mixing zone and another portion downwardly within the mixing zone. Alkylated product is then recovered from the downstream side of the reaction zone. In a preferred embodiment of the invention, the aromatic substrate is benzene and the alkylating agent is an ethylating agent such as ethylene. In a further embodiment of the invention, the quench fluid is supplied to the mixing zone through a plurality of dispersion channels which are spaced laterally from one another and extend transversely across the mixing chamber. At least some of the dispersion channels dispense the quench fluid alternately, upwardly and downwardly within the mixing zone. Preferably, the dispersion channels are located within the upper one-half of the mixing zone.
In a further embodiment of the invention, a multi-stage alkylation reaction zone is provided within an elongated reactor having an upper catalyst bed extending transversely of the reactor and at least three subsequent catalyst beds extending transversely of the reactor and spaced from one another. Spacing between the catalyst beds provides an upper mixing zone between the first catalyst bed and the next adjacent catalyst bed and subsequent mixing zones between the succeeding catalyst beds. Sparger systems are provided in the mixing zones incorporating a plurality of laterally-spaced dispersion channels. A mixture of the aromatic substrate and the alkylating agent is supplied to the sparger systems to provide a plurality of flow paths through linearly-spaced orifice outlets in the dispersion channels directed upwardly and downwardly within the mixing zone.
In accordance with yet another aspect of the invention, there is provided an alkylation reactor comprising an elongated reactor vessel having an inlet for the supply of reactants and an outlet for the withdrawal of product from the vessel. A plurality of catalyst beds are provided along the length of the reactor with a plurality of sparger systems each comprising a plurality of laterally displaced dispersion tubes and a manifold or header connecting the spaced dispersion tubes to provide for the supply of feedstock there too. At least some of the dispersion tubes have openings along the lengths thereof in which the openings alternately open in a downward and an upward orientation to dispense feedstock into the mixing zones.